Packet data communication systems are known in both the wireless and wireline environments. In the wireless environment, a packet data system includes packet data routers, data controllers, base stations, and wireless communication units (e.g., mobile radios, portable radios, radiotelephones, or wireless data terminals). In the wireline environment, a packet data system includes switches and wireline communication devices (e.g., personal computers, computer servers, mainframes, laptop computers, personal communication devices, or custom data terminals). Packet data communications are also known to exist between wireless and wireline systems.
Packet data systems typically provide for transmission of data packets either individually or in groups otherwise known as "bundles." In systems that provide for individual packet transmission, such as transport control protocol (TCP) systems, the sending device transmits one packet at a time and receives a corresponding acknowledgment for each packet from the receiving device. Each data packet includes a packet sequence number that allows the receiving device to determine which packet it has received. Knowing the packet sequence number of the received packet, the receiving device transmits an acknowledgment indicating the packet sequence number of the packet that was received. In systems that provide for the use of selective automatic repeat request (SARQ) protocols, the data packet is typically subdivided into data blocks, wherein each data block has an associated data block number. In such SARQ systems, the acknowledgment typically includes the packet sequence number and the data block numbers of the data blocks that were not completely received by the receiving device. Thus, in SARQ systems, the sending device need only retransmit the unreceived data blocks instead of the entire data packet.
In systems that provide for group packet transmissions, the sending device transmits a group of data packets and receives a single acknowledgment for the group of data packets. As in single packet transmission systems, each data packet includes a packet sequence number. However, in group transmission systems, the acknowledgment includes the packet sequence number of each data packet in the group that was not completely received by the receiving device and, when an SARQ protocol is used, the data block numbers of the data blocks in each packet that were not completely received by the receiving device. To distinguish between acknowledgments for groups of data packets, the sending device typically identifies the lowest-valued packet sequence number of the group being acknowledged and compares it to the packet sequence numbers stored in a database that associates packet sequence numbers with group numbers. For example, when the sending device transmits Group 1 having packet sequence numbers 1-5, it stores the group number (1 in this case) and the packet sequence numbers (1-5 in this case) in a database. If, before receiving an acknowledgment of 1, the sending device also transmits Group 2, consisting of packet sequence numbers 6-10, and then receives the acknowledgment, the sending device examines the acknowledgment to determine which data packets are being acknowledged. Thus, if the acknowledgment indicated that data blocks 2 and 3 of the data packet having packet sequence number 4 were not received, the sending device would determine that the acknowledgment was an acknowledgment of Group 1 because packet sequence number 4 was transmitted in Group 1.
In both single packet and group packet transmission systems, acknowledgment timers are employed to set retransmission times. When an acknowledgment to a particular transmission is not received within the predetermined time of the corresponding acknowledgment timer, the sending device presumes the transmission was not received and retransmits the packet or group of packets, respectively. However, when an acknowledgment is received subsequent to the retransmission, the sending device does not know which transmission the acknowledgment actually corresponds to and presumes that the acknowledgment corresponds to the retransmission. Such a presumption may be in error due to inherent delays in the packet data system. For example, in integrated voice and data systems, voice calls typically have priority over data calls. Thus, a situation may arise whereby a receiving device receives a packet data transmission, but, before the receiving device can respond with an acknowledgment, the system preempts the device's request for allocation of a channel over which to transmit the acknowledgment due to high levels of voice traffic. As a consequence of the delay in transmitting the acknowledgment, the sending device's acknowledgment timer expires and a retransmission occurs.
By not knowing which transmission the acknowledgment actually corresponds to, the sending device, in response to the acknowledgment, might retransmit data that was already received by the receiving device (e.g., when the acknowledgment is an acknowledgment of the original transmission and indicates fewer completely received packets than were received in the retransmission). By retransmitting data that was already received, the sending device is inefficiently using a communication channel that could otherwise be used to transmit new or otherwise unreceived data.
One approach that could be used to eliminate the uncertainty in acknowledgments is to include a group identifier in each transmission and corresponding acknowledgment. By incrementing the group identifier with each transmission and retransmission, the receiving device can easily determine which group it is acknowledging. By including the group identifier in each acknowledgment, the sending device can easily determine which group is being acknowledged. However, although including a group identifier solves the aforementioned acknowledgment identification problem, it does so at the cost of reduced data throughput. Since communication channels have fixed bandwidths, adding bits to identify the transmission group would result in correspondingly fewer bits of data in each transmission, thereby reducing throughput.
Therefore, a need exists for a method and apparatus of conveying data packets in a packet data communication system that solves the acknowledgment identification problem, without reducing data throughput.